[QueueRunner] Support "thenables" returned by tests

[aleclarson]

This commit allows done or done.fail to be called by a returned promise/thenable.

This reduces the following boilerplate:

• promise.then(done)
• promise.catch(done.fail)

Includes tests for resolved promises and rejected promises.
Should I include one for pending promises, too?

Example

it(() => {
  return fetch('http://www.google.com')
    .then(res => expect(res).toBe(...));
});

• If the returned thenable is resolved, the done function is called.
• If the returned thenable is rejected, the done.fail function is called.

Failure tests

To test failure cases, you can catch the error and call expect(error.message).

it(() => {
  return fetch('bad url')
    .catch(error => expect(error.message).toBe(...));
});

[aleclarson]

Am I not allowed to use setImmediate in the tests?

[aleclarson]

Fixed an edge case where the promise variable was being carried over to the next iteration, resulting in an error being thrown TypeError: promise.then is not a function.

Let me know if there are other issues. 👍

[BenoitZugmeyer]

Disclaimer: I'm not related to Jasmine in any way, just an enthusiastic user.

This feature is quite popular and has been discussed and PR'd many times (PR #202, #681, PR #696, #923, PR #1029), and has always been rejected with the following workarounds:

• You can just pass done and done.fail as callbacks to .then
• If you are into coroutines, you can use jasmine-co
• You can use jasmine-promises

In my opinion, it would be a great addition to Jasmine:

• Most other popular test runners (mocha, jest, ava, ...) are supporting asynchronous tests via promises out of the box. It seems like a new consensus, like the done() callback a few years ago. It would help migrations from one test runner to another, and build tools/helpers compatible with multiple test runners.
• Coroutines were alright a few years ago, but now that async/await functions are standardized and supported by Node (last stable version) and some browsers out of the box, there is not much reason to use them anymore. With support for tests returning promises, jasmine would support async functions without any extra code.
• The jasmine-promises doesn't support nodejs (at the moment) and seems a bit abandonned to be honnest (nodejs support is on the master branch, but no release has been done for six months).
• Adding promises support is straightforward and wouldn't add much code, and no extra dependency.

As a side note, @aleclarson : your PR breaks the CI build because of lints reported by jshint (https://travis-ci.org/jasmine/jasmine/jobs/202125138#L380)

[aleclarson]

@BenoitZugmeyer Thanks for the heads up! All fixed.

I'll squash the commits once a maintainer speaks up about any nits.

[slackersoft]

In general the plan seems good for this, but there are a couple issues with the current testing strategy related browsers that don't support certain features natively.

Additionally, the build for this PR is broken for your new tests, so that would need to be fixed as well.

[slackersoft]

Jasmine's tests need to run in IE 8+ and PhantomJS (as well as Edge, Chrome, Firefox, and Node.js) so we can't use bare Promise directly in specs for browsers that don't support them.

[slackersoft]

Similarly, setImmediate isn't available in all browsers that Jasmine supports and as such can't be used in Jasmine's tests.

[slackersoft]

Native Promise as above

[slackersoft]

setImmediate as above